The Toyota Prius Plug-In Hybrid was last year's second best-selling plug-in car, but it's been on a downward trend this year.

In April, just 599 were delivered, for a year-to-date total of 2,952. That's the lowest monthly sales number since the very first month the plug-in Prius went on sale, in March 2012.

The 2014 Honda Accord Plug-In Hybrid logged 55 deliveries in April, more than its total of 45 deliveries in the three months since it went on sale in January. Sales are rising as Honda cautiously rolls out its first-ever plug-in hybrid vehicle in California.

Ford sold almost as many of its pair of Energi plug-in hybrids this month as last, but the mix shifted.

The C-Max Energi fell to 411 from last month's 494, while deliveries of the Fusion Energi rose to 364 from 295 in March.

Compliance cars

Finally, there are the California "compliance cars," those battery-electric vehicles built only in sufficient numbers to satisfy that state's zero-emission vehicle sales mandates.

First to report was the Honda Fit EV, whose 22 deliveries were essentially identical to last month's 23, for a year-to-date total of 68 and a lifetime total of 161 since last July.

After a burst of 133 sales last month for the Toyota RAV4 EV, its numbers fell back to its average levels: during April, 70 of the compact crossovers with Tesla powertrains were delivered.

Ford sold 147 of its Focus Electric hatchback, down on the 180 it sold last month, bringing the total for the first third of the year to an unimpressive 466.